1. Field of the Invention
The present invention relates to a cut core which comprises a thin strip of magnetic amorphous alloy and which is used for various kinds of inductors and transformers. The present invention also relates to a method for manufacturing the cut core.
2. Description of the Prior Art
As is well known, the cores of inductors or the like are either wound or laminated cores. When the cores are manufactured by using a thin strip of magnetic amorphous alloy, such thin strip is wound, i.e., wound bodies are produced, in the light of the productivity of the cores. The wound bodies are cut into U-, C-, or I-shaped pieces. Usually, a pair of the so-produced cut pieces is connected either with a spacer or without a spacer to form a core, in which the cut end of one of the cut pieces faces the cut end of the other cut piece. Occasionally, for example, an I-shaped cut piece is connected with a C-shaped cut piece to form a D-shaped core, the cut ends not facing one another. Such core including a cut end(s) and comprising a thin strip of magnetic amorphous alloy is hereinafter referred to as an amorphous cut core.
According to a conventional method for manufacturing an amorphous cut core, a thin strip of magnetic amorphous alloy is wound into a toroidal form, and the wound body is impregnated with resin, is mounted in a casing or is fixed with a caulking member such as a bobbin, and is then cut into a predetermined shape. Alternatively, two or more wound bodies are formed and then fixedly bonded to each other, and the bonded wound bodies are then cut into a predetermined shape. The wound and cut bodies described above are then polished by rotational polishing so as to smooth their cut ends. This polishing disadvantageously results in an increase in the watt loss and a decrease in the permeability of the amorphous cut core and in an eddy current loss or the generation of interlayer short-circuiting at the cut ends.
It is known in a method for manufacturing cut cores from a silicon steel that the silicon steel sheet is wound, cut, polished, lapped, and chemically polished by etching (Technical Report of the Electric Society (Second Section) Vol. 25, pp 1.about.15, December 1973). The polishing carried out is rotational polishing or straight polishing across the layers of silicon steel. In this known manufacturing method, the cut ends of the wound body are closely contacted by lapping and polishing so that the watt loss generated at the cut ends is lessened. The lapping and polishing applied to a cut core made of silicon steel cannot be applied to an amorphous cut core for the following reasons.
The packing factor of a wound core made of a silicon steel sheet is from 96% to 97% and is higher than that of an amorphous cut core. Since an amorphous alloy sheet is thin, for example, approximately 20 .mu.m in thickness, and the surface thereof is rougher than that of a silicon steel sheet, which is cold-rolled in the final rolling step, the packing density of the amorphous cut core is low, e.g., from approximately 75% to approximately 83%. Due to the low packing density, gaps are formed between the neighboring layers of the amorphous cut core. The lapping liquid and the etchant of chemical polishing penetrate through the open ends into the interior of the gaps. The so-penetrated lapping liquid and etchant of chemical polishing remain within, and cannot be extracted from the gaps. The liquid and the etchant, particularly a hydrochloric acid- or nitric acid- based etchant, secularly deteriorate the magnetic properties of the amorphous cut core. Since the lapping and chemical polishing disadvantageously result in the penetration of the liquid and the etchant into the amorphous cut core, conventionally, the rotational polishing described above is employed for producing an amorphous cut core. Rotational polishing is conventionally carried out only to such an extent that the burrs formed during cutting are removed only to a certain extent.
However, it is difficult to satisfactorily smoothen the burrs by rotational polishing since an amorphous alloy is elastic and ductile. Also, rotational polishing can disadvantageously result in an increase in the watt loss and an eddy current loss and a decrease in the permeability of an amorphous cut core or the generation of interlayer short-circuiting at the cut ends.